Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device and a fabrication method of the in-plane switching mode liquid crystal display device which has a low pretilt angle by applying a three-electrode structure to an in-plane switching display and mixing a photocurable polymer into an alignment film by a rubbing process.
Description of the Related Art
A liquid crystal display device is one of flat panel display devices and configured to control an amount of light to be transmitted by applying a voltage to an electrode and rearranging liquid crystal molecules in a liquid crystal layer.
Among various liquid crystal modes, an FFS (Fringe Field Switching) mode has been widely used as a liquid crystal mode with a high transmittance and a wide viewing angle.
The FFS mode refers to a mode of rotating liquid crystal molecules using an in-plane electric field in a single substrate on which a common electrode and a pixel electrode are formed in sequence.
FIG. 1 illustrates a basic structure of an in-plane switching mode liquid crystal display device using a two-electrode structure.
A structure of an in-plane switching mode liquid crystal display device of the prior art includes a liquid crystal layer 30 between an upper substrate 10 and a lower substrate 70 on which a lower plate conductive electrode 60 is deposited, as illustrated in
FIG. 1.
Herein, a pattern electrode 40 is additionally deposited on the lower substrate, and an insulating layer 50 is disposed between the lower plate conductive electrode 60 and the pattern electrode 40.
FIG. 2 illustrates a liquid crystal alignment method of the in-plane switching mode liquid crystal display device of FIG. 1.
As illustrated in FIG. 2, a rubbing roller 100 wound with a rubbing cloth is rotated on the substrate on which an in-plane alignment film 20 is formed. In this case, polymer chains formed within a surface of the alignment film 20 are aligned in one direction by a contact between the substrate and the rubbing cloth.
Herein, a pretilt angle defined as an angle formed between a major axis of the liquid crystal molecules and a surface of the substrate when the upper and lower substrates are bonded to each other is about 1 to 3 degrees.
As illustrated herein, in the in-plane switching mode liquid crystal display device of the prior art, if the liquid crystal molecules are aligned by a rubbing process, a pretilt angle is about 1 to 3 degrees, which causes a light leakage in a black state.
A light leakage caused by a pretilt angle cannot be improved by viewing angle compensation using a compensation film and thus causes a serious deterioration in performance of a display.
Particularly, studies for achieving a wide viewing angle have been actively conducted as a demand for a high-resolution and high-performance display has rapidly increased. In this case, a pretilt angle of a liquid crystal greatly affects a viewing angle.
In order to improve a viewing angle, studies for designing a viewing angle compensating structure and lowering a pretilt angle have been actively conducted. As one of the studies, a study of photo alignment using strong UV rays has been conducted, but has not yet been applied to mass production due to many disadvantages.
As such, visibility is a very important factor in a current liquid crystal display device. Therefore, development of a technology capable of improving the visibility of the in-plane switching mode liquid crystal display device of the prior art has been demanded.
In particular, development of a technology capable of improving the visibility without deterioration in other electro-optic characteristics has been demanded.